One-Third of Cambodians Infected With Threadworm

By Will Boggs MD

July 22, 2019

NEW YORK (Reuters Health) - Nearly a third of Cambodians have been infected with the threadworm Strongyloides stercoralis, according to a nationwide, community-based parasitological survey.

"We knew that the prevalence was high, but we were not expecting a 30% infection rate in the general population," said Dr. Peter Odermatt from the Swiss Tropical and Public Health Institute and the University of Basel, in Switzerland.

"Threadworm (Strongyloides stercoralis) infection is per se a health risk - particularly in individual who are immunodepressed and other risk groups, such as older people, alcoholics, etc., where the infection may develop as a systemic infection," he told Reuters Health by email.

S. stercoralis has been recognized as a public health problem in Cambodia, but the national prevalence and the location of high-risk zones were unknown.

Dr. Odermatt and colleagues used a test recently developed in Thailand that detects antibodies in urine to undertake a national parasitological survey in all provinces of Cambodia in 2016.

Overall, the prevalence of S. stercoralis was 30.7%, ranging from 10.9% in Prey Veng province of 48.2% in Koh Kong province.

The prevalence was highly variable at the village level, ranging from 2.9% to 88.9%, the report in PLoS Neglected Tropical Diseases, online June 20.

Risk factors for infection included open defecation by participants, increasing nighttime land surface temperature during dry season, increasing minimum annual rainfall and increasing distance to water. The odds of infection were lower among participants living in villages located in croplands.

"For the first time a national Strongyloides risk map could be developed," Dr. Odermatt said. "The new urine test developed by the Thai researchers and the geospatial modeling developed by our Swiss partners led to that success. As a consequence, we can calculate the exact number of people who need treatment and, hence, planning of national intervention is possible."

"Most endemic countries do have national helminth control programs against soil-transmitted helminths," he explained. "However, they do not include Strongyloides as target infection because (i) they have often not enough information about the exact infection burden because they have not introduced the diagnostic test, and (ii) they do not have the funding to provide ivermectin treatment. Hence, subsidies or other financing mechanisms are required (so) that (the) poorest populations obtain the treatment."

"More resources should be given to World Health Organization (WHO) in order that it can support the endemic countries to fully target this most neglected parasite," Dr. Odermatt said.

He added, "Traveling in low- and middle-income countries may put travelers at risk for an infection with S. stercoralis, and this risk is higher than previously thought. Hence, physicians should be aware of this fact. In addition, physicians should be aware that a specific diagnostic technique is required to diagnose the infection with a high sensitivity. Strongyloides infection may lead to lifelong infection. Treatment with ivermectin is efficacious but confirmation of success is advised."


PLoS Negl Trop Dis 2019.